Brian is maintaining office space at both the LA and London Henson offices. If you go to the Henson web site and choose company executives, you will see that Brian is still listed, though no longer has a title.

No idea what that means in terms of the actual day to day operations....

It's a good thing he's still with JHC casuse after all, it belonged to his gifted father. I have two questions. Is Brian also stepping down in order to re build the Company? Does JHC still provide materials and performers for Sesame Street despite Sesame Workshop's control over all the characters?

I don't know the answer to your fist question but Henson does still supply the puppets and performers for SS All of the regulars, Spinney, Nelson, Brill, Clash, robinson, rudman, Mazzarino, etc. are all still employed by Henson and sent to work on SS although, since the characters are now owneed by Sesame wokshop it's a little confusing (or so I hear).